1. Field of the Invention
The present invention relates to the treatment/conversion of "oxygen-rich" exhaust gases by means of spinel-based catalysts, for reducing emissions of the oxides of nitrogen ("NO.sub.x ").
2. Description of the Prior Art
Emissions of oxides of nitrogen, NO.sub.x, from exhaust gases, in particular from automotive engines, can be reduced by "three-way" catalysts which utilize, stoichiometrically, the reducing gases present in the exhaust mixture. Any excess oxygen results in a severe deterioration of catalyst performance.
Certain engines, such as diesel engines or lean burning engines, economize on fuel, but emit exhaust gases which permanently contain a large excess of oxygen, for example an excess of at least 5%. A standard three-way catalyst is thus of no value for the conversion of NO.sub.x emissions from these engines. Further, limiting NO.sub.x emissions has become imperative because of the increasingly strict regulations governing automotive exhaust emissions which now cover this type of engine.
Serious need thus exists in this art for an effective catalyst which can improvedly reduce NO.sub.x emissions.